Near Field Communication (NFC) is a wireless communication technology which helps electronic devices receive and transmit electromagnetic waves by means of magnetic field induction to perform short-distance communication. The technology can provide consumers with simple and visual information exchange, content access, and services. Due to such characteristic, NFC technology has drawn more and more attention, and has been applied to mobile devices, PCs, smart control units, etc.
For application of traditional NFC hand-held devices, an NFC antenna radiator is generally placed on a battery, and in order to reduce the negative effects of eddy currents on the NFC antenna, which are generated on the battery and are opposite to the current direction of the antenna itself, a ferrite layer which can separate the antenna coil from the battery is placed between the NFC antenna coil and the battery at the same time. To ensure the performance of the NFC antenna, the NFC antenna employing such design solution must meet certain size requirements. The antenna in the traditional NFC antenna solution is relatively large in size and therefore fails to meet the miniaturization demand of hand-held devices.
In order to fulfill the aim of reducing the size of the NFC antenna, Murata Manufacturing Co., Ltd. has put forward a small-sized surface mounted type NFC antenna solution in Chinese Patent CN103620869A, and displayed the specific applications of the solution in actual communication devices in Chinese patent CN102959800B. Compared with the traditional NFC antenna solution, the biggest difference of such solution lies in that the traditional NFC antenna coil with a relatively large size is spirally wound on a ferrite core with a very small size to form a spiral tubular antenna. After the small-sized NFC antenna monomer is placed above and effectively coupled with a metal sheet (or a PCB), an eddy current with a positive effect is generated on the metal sheet to further improve the performance of the whole antenna system (including the surface mounted type NFC antenna and the metal sheet). Compared with the traditional large-sized NFC antenna solution, the NFC antenna solution put forward by Murata Manufacturing Co., Ltd. has made huge progress in the aspect of antenna size. However, such surface mounted type antenna has a defect: when the antenna monomer is placed on the PCB or metal sheet, due to the special winding mode of the antenna coil on the ferrite, the magnetic field generated on the antenna itself is vertical and orthogonal to the magnetic field generated by the effective eddy current which is generated on the metal sheet. Such mutual vertical and orthogonal relationship of the magnetic fields lowers the performance of the whole antenna system.
In order to improve the performance of the NFC antenna, Chinese patent 201610076899.4 discloses an orthogonally wound surface mounted type NFC antenna and an antenna system. The NFC antenna comprises a ferrite core which is formed by superposing a plurality of plate-like ferrite units and extends along the X-Y plane, a first coil and a second coil of the NFC antenna that are orthogonally and annularly wound on the ferrite core, wherein the first coil is spirally wound along the −X axis or +X axis direction; the second coil is spirally wound along the +Z axis or −Z axis in the vertical direction; and the tail end of the second coil is connected with the head end of the first coil. For the orthogonally wound surface mounted type NFC antenna disclosed by the patent, the performance of the NFC antenna is improved to a certain degree through superposition of (B1) and (B2). However, every turn of the second coil is crossed with the first coil, so the horizontal magnetic field generated by the first coil and the vertical magnetic field generated by the second coil perform relatively strong back-coupling which weakens the magnetic field of the second coil. By such configuration mode, the antenna and the metal sheet cannot reach the optimal matched state.
Therefore, it is necessary to make an improvement on the aforementioned surface mounted type NFC antenna and develop a small-sized surface mounted type NFC antenna which has high performance and can be optimally matched with the magnetic field generated by the eddy current which is generated on the metal sheet.